Inside This Unit: The Full Breakdown
This unit builds electrostatics: charge and Coulomb’s law, electric fields and field lines, and electric potential and potential energy.
Why it matters
Electrostatics is the most heavily weighted unit and underpins circuits, magnetism, and modern physics. Mastering fields and potential is essential.
Key concepts
- Coulomb’s law (F = kq₁q₂/r²) gives the inverse-square force between charges.
- The electric field E = F/q points away from positive and toward negative charge.
- Electric potential V = U/q; work to move a charge is W = qΔV.
- In conductors, excess charge resides on the surface and the interior field is zero.
Charge, Force, and Field
Charge is conserved and quantized; like charges repel and opposites attract via Coulomb’s inverse-square law. The electric field is force per unit charge, visualized with field lines whose density indicates strength. Between parallel plates the field is uniform with E = V/d.
Potential and Energy
Electric potential is potential energy per unit charge; moving a charge through a potential difference does work W = qΔV. No work is done along an equipotential surface. In electrostatic equilibrium, conductors have zero interior field and excess charge on the surface.
AP exam tip
Keep field (vector, N/C) and potential (scalar, volts) distinct — many errors come from treating potential as a vector or confusing E with V.
Connections to other units
- Unit 4: Potential difference drives current in circuits.
- Unit 5: Moving charges create and respond to magnetic fields.
